1. Field of the Invention
The present invention relates to a fluoroelastomer and its cross-linkable composition, and more particularly to a fluoroelastomer capable of giving vulcanization products having distinguished low temperature characteristics, solvent resistance and chemical resistance, and its cross-linkable composition.
2. Description of Related Art
JP-A-3-100,039 disclosing an invention made by the present applicant teaches a terpolymer comprising about 5 to about 30% by mole, preferably about 10 to about 25% by mole, of tetrafluoroethylene, about 10 to about 30% by mole, preferably about 20 to about 30% by mole, of perfluoro(methyl vinyl ether) and about 50 to about 80% by mole, preferably about 50 to about 60% by mole, of vinylidene fluoride, the sum total being 100% by mole. Comparative Example 4 thereof shows that a terpolymer of tetrafluoroethylene/perfluoro(methyl vinyl ether)/vinylidene fluoride (molar ratio: 15:25:60, which falls within a preferable copolymerization composition ratio of these comonomers) has distinguished low temperature characteristics such as a TR-10 value of -24.degree. C., but at the same time it points out poor solvent resistance and chemical resistance due to incorporation of much vinylidene fluoride having a poor chemical resistance in the terpolymer.
Thus, the above-mentioned JP-A-3-100,039 tries to improve the low temperature characteristics, solvent resistance and chemical resistance by blending the terpolymer with a copolymer of tetrafluoroethylene/perfluoro(methyl vinyl ether), where the resulting blend has such a blending proportion as about 1 to about 50 % by weight of the terpolymer and about 99 to about 50% by weight of the copolymer. That is, it cannot be denied that the former terpolymer is used rather as a modifying agent of the latter copolymer.